Page:Mexico in 1827 Vol 1.djvu/38

12 nearer approach to the Pacific side, (where the air is perceptibly milder;) the want, or abundance, of water; all these are circumstances which affect the temperature in the most opposite manner, even at the same height, and in the same parallel; and thus render it impossible, by the standard of elevation alone, to form any exact idea of the climate of the Table-land. Humboldt mentions the valley of Rio Verde, where sugar is raised with success at near four thousand feet above the degree of elevation which previous experiments had induced him to fix, as productive of the minimum of heat requisite for its cultivation; and I have myself seen a little spot, in the vicinity of Guădălajāră, which presents a similar phenomenon. In addition to these local peculiarities, which occur without there being any sensible difference in point of elevation to occasion them, every little break or descent in the surface of the Table-land, leads as naturally to an increase of heat, as the ascent from the coast does to a diminution of it. The transition is sometimes extremely sudden, for a deep ravine, or căñādă, is sufficient to occasion it. Thus, in the Căñādă of Qŭerētărŏ, and in the famous Barranca of Rēglă, at Real del Monte, both of which are situated in the centre of the Table-land, and nearly upon the same level as the Capital, a few-hundred yards change the face of nature entirely.